Labeling containers by applying preprinted film labels is becoming an increasingly popular alternative to conventional lithography. Various environmental problems, including air pollution and recycling concerns strongly favor adoption of preprinted films for labeling containers. Plastic containers, metal cans and glass bottles can be labeled effectively with film labels.
Cost considerations have led to the development of thin films which have the advantage of reducing the cost of materials used but require increasingly more stringent process controls to allow high speed labeling equipment to handle thin, stretchable, and relatively flimsy labeling materials.
Labeling speed is an important consideration in high production canning and bottling plants, since it is unacceptable for labeling processes to impede productivity of a bottling or canning line. Labeling speed is of paramount importance with labeling speeds in excess of ten containers per second being possible to achieve with some labeling materials. Generally, thicker materials that are resistant to stretching are easier to handle by conventional labeling machines.
When thin labeling materials are run at high speeds, problems, such as label splitting, stretching labels and misalignment of labels, are encountered. With roll fed labels, when the labels are cut from the web of label material, excessive tension on the label can cause the labels to split instead of being cut. Similarly, overtensioning thin labels can cause the labels to stretch as they are applied to the vacuum drum. As the labels are transferred to a vacuum drum, excessive vacuum can cause the label segment to shift or snap leading to misaligned labels on the containers.
Some labeling materials include coatings or treatments that result in higher coefficients of friction that can interfere with the labeling process. Labels having a higher coefficient of friction tend to become overtensioned more easily which aggravates problems associated with overtensioning.
Another problem encountered when labels are supported by a vacuum drum during the labeling process is that glue applicators for applying glue to the label segments can become jammed by labels if insufficient vacuum is provided to prevent the labels from following the glue applicator.
With roll fed labeling operations, a vacuum label retention system on a label cutter may be used to hold the end of the label material web while segments are cut-off prior to supplying the segments to the vacuum drum. It has been found that the vacuum port location on the cutter drum can be set to increase vacuum at the point which the label web is fed to the cutter while decreasing vacuum pressure at the cut-off knife location.
Utilization of a single vacuum source for both the cutter and vacuum drum can cause variation in vacuum pressure that can lead to slippage or jamming of labelling.
The primary objective of the present invention is to provide a labeling system utilizing a plurality of cavities for providing different levels of vacuum, wherein thin films can be swiftly and accurately applied with minimum scrap or wastage.
It is another object of the invention to provide a method of labeling containers, wherein ultra-thin stretchable film can be applied without reducing labeling speeds or overtensioning label material during the labeling process.
These and other objects of the invention are achieved by the novel and useful methods of the present invention.